Process and device for recognizing foreign bodies in viscous or fluid, lump-containing foodstuffs

ABSTRACT

A process and device are disclosed for recognizing foreign bodies in viscous or fluid masses with lumpy foodstuffs. The mass to be checked runs through a measurement section, in which, pulsed ultrasonic signals are emitted through the mass, are reflected after passing through the mass, and after passing again through the mass they are received and compared with the ultrasonic echo of the reflection surface. When the changes of the received signals exceed a predetermined threshold value, a warning or actuating signal is generated to interrupt mass advance. The parameters to be evaluated for the signal may be their amplitudes, as well as the speed of change of their amplitudes or the propagation times.

This is a continuation-in-part of application Ser. No. 08/557,058, filedMar. 11, 1996, now abandoned, which is a 371 of PCT/EP94/01623 filed May19, 1993.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention refers to a method for detecting foreign bodies in liquidor solid material masses, especially in foods, as wall as to a devicefor implementing this method.

2. Description of the Prior Art

Numerous foods, especially milk products, e.g. yoghourts as well as babyfood, are often produced on large scale in industrial manufacturingprocesses. Before filling the finished foods, a thorough examination forany foreign bodies possibly existing is required among other tasks.These foreign bodies can get into the foods during the productionprocess on the one hand, or, on the other hand, they can exist inindividual ingredients, e.g. fruit.

Within fish processing, light tables are used, e.g. for examining fishfillets. For obvious reasons, however, these tables are not suitable forexamining the foods mentioned above and, in addition, they have thedisadvantage that the actual testing is made by visual inspection and itcannot therefore be automated.

Moreover, there are known X-ray apparatuses using X-rays according tothe same principle in which the visual inspection is made via a displayscreen. This method has one additional disadvantage, viz. thecorresponding working places are subjected to increased intensity ofradiation.

From DE-OS 40 13 402, a process for the detection of gas bubbles inliquid-filled pipes is known, as well as the device needed for thisprocess, in which a transmitter and a receiver are positioned on eitherside of the pipe and transmit single impulses fixed in length and levelto determine the presence of gas bubbles within the pipe through thechange in the impulses after traversing the liquid. This well-knownprocess is not suitable for the examination mentioned above since it canonly detect a gas phase within a liquid phase. The difference in densitybetween gas and liquid is much higher than that between foreign bodiesand food (viscose mass and liquid mass).

From the magazine “Elektronik”, Nr. 25/1991, a “particle detective” isknown that works with high frequency ultrasound according to the(Doppler) principle. The disadvantage of this method is that it again isvery work-intensive and cannot be automated.

Finally, in U.S. Pat. No. 4,607,520, a process and a device for thedetection of bubbles in a flow of liquid is described. For this process,ultrasound impulses are sent through a designated segment of the liquidto be examined. During a time frame that is opened after the impulserunning time, it is checked whether the impulses reached the receiver.If this is not the case, it is assumed that there is a lack of homogency(a gas bubble) within the designated segment. Again, this process is notsuitable for the testing of food for any foreign body contents.

The invention was therefore based on the requirement to specify a methodfor detecting foreign bodies in viscous or liquid material masses,especially in foods, as well as a device for implementing this methodand also enabling automated testing.

SUMMARY OF THE INVENTION

As to the method, this requirement is met by continuous conveying of thematerial mass at predetermined speed through a measurement line section,by the transmission of ultrasonic signals through the material masstransported in the measurement line section, by the reception of thetransmitted ultrasonic signals after passing through the material mass,by a comparison of at least one received ultrasonic signal with at leastone transmitted ultrasonic signal for detecting variations of at leastone predefined signal parameter, as well as by generating an alarmand/or activation signal when the variation of at least one signalparameter exceeds or falls short of a predetermined limit value, inorder to interrupt the material transport and/or to divert the materialmass from the transport flow.

Foreign bodies can be recognized quite easily even if the foods screenedare not homogenous, but contains solid pieces, as long as the length andfrequency of the ultrasound impulses transmitted are predetermined. Inthat case, a weakening in amplitude without a change in duration of theimpulse signals the presence of a foreign body, whereas the presence ofe.g. a piece of fruit or another form of concentration as well as alowering in the concentration of sugar would cause a change in durationof the signal as well as a weakening in amplitude.

One especially advantageous development of this process is to warm upthe mass to be tested before running the examination. This method leadsto improved results, especially in goods containing pectine, where theforeign bodies (i.e. seeds) are much better discernable from solidpieces of food (i.e. pieces of fruit).

The process preferably also contains an adaptive reinforcement of theultrasound signal/s and/or an adaptation of the border value/s. Thisallows for an optimum adaptation to the permeability and consistency ofthe good to be examined.

Finally, it is also possible to control the amplitudes of the sentultrasound signals in such a way that the amplitudes of the receivedultrasound signals are constant, where the change in manipulatedvariable is compacted to the predetermined border value. The ultrasoundsignals are preferably pulsed, so that the running time betweentransmitter and receiver provides an additional controlling value.

The device according to invention comprises at least one ultrasonictransmitter and at least one ultrasonic receiver, with the measurementline section being led through between the transmitter and the receiver.As an alternative to this, the device can also have a reflector fromwhich the ultrasonic signals are reflected after passing through themeasurement line section, pass through the measurement line again, andare finally picked up by the receiver(s). A wall of the measurement linesection, e.g. a tube wall, can likewise be used for sound reflection.

One advantage of these solutions lies in the fact that the applicationof ultrasonic signals leads to no radiation exposure of the environmentand that they can be implemented at very low cost because thetransmitter and receiver elements, as well as the evaluation unit,require no costly safety provisions, and because generally availablestandard products can be used. Apart from this, it is quite easy to makea fail-safe test setup for ultrasonic testing due to the fact thathigh-frequency acoustic signals generally do not exist in theenvironment at all—or they only exist with very low intensity—and theycan be easily screened.

In addition, the power consumption of a corresponding device accordingto invention is very low in comparison with the known devices or methodsmentioned.

One of the predetermined signal parameters is preferably the amplitudeof the ultrasonic signals.

Besides, the speed of the variation of amplitude of several ultrasonicsignals received successively can also be used as an additional oralternative signal parameter.

Furthermore, a signal parameter—preferably the amplitude of thetransmitted ultrasonic signal—can be controlled in such a way that theamplitude of the received signal remains constant, with the variation ofthe manipulated variable being compared with a predetermined limitvalue.

It is also possible to modulate the transmitted ultrasonic signals andto evaluate a phase displacement between the transmitted and thereceived signal as signal parameter.

The preferred method for detecting foreign bodies, which influenceultrasonic signals in quite different ways, is either to use severalultrasonic transmitters operating at different frequencies, or totrigger an ultrasonic transmitter so that its frequency always covers apredefined frequency band.

Several single transmitters and, if applicable, the receiver allocatedto each transmitter are preferably Clocked individually in order toavoid mutual interferences.

If the material mass to be tested is filled in receptacles, with thereceptacles being formed in a second material mass within themeasurement line section, foods that are already packed can also betested for foreign bodies. In this case, the second material mass servesas a transmitting medium for acoustic signals which pass through thereceptacle and the foods contained therein.

The device according to invention is preferably integrated into afilling and/or packing system, in which case the device is provided witha downstream switch by means of which the transported material mass orreceptacle is diverted when the activation signal is generated.

Further details, characteristics and advantages of the invention resultfrom the following description of execution examples based on a drawing.

BRIEF DESCRIPTION OF THE PREFERRED DRAWINGS

The following are shown:

FIG. 1 a block diagram of a device according to invention forimplementing the method and

FIG. 2 a flow diagram of the operational mode of a device forimplementing the method.

DESCRIPTION OF THE PREFERRED DRAWINGS

According to FIG. 1, a conveying line 1 has been provided for thematerial mass (foods) to be tested. At the input end of the conveyingline 1 there is a pump 3 which is triggered by a signal processing unit5. The material mass to be tested is transported through a measurementline section 2 and, after that, it is either fed to a packing stationvia a valve 4 or diverted from the transport flow if foreign bodies weredetected in the material mass in the measurement line section. The valve4 is switched over with the signal processing unit 5, for example byactuating a solenoid valve 41 The data acquired in the measurement linesection are processed and evaluated as usual in the signal processingunit 5.

The measurement line section 2 contains one or several pairs ofultrasonic transmitters 21 and ultrasonic receivers 22. The executiontype shown here is provided with several ultrasonic transmitters 21 andseveral ultrasonic receivers 22, mainly placed side by side on one sideof the transport flow. Arranged on the other side of the transport flowis a reflector 23 from which the signals emitted by one transmitter Z1toward the allocated receiver 22 are reflected in each case. Thecorresponding transmitter-receiver pairs in each case are preferablytriggered (clocked) successively in order to prevent mutualinterferences. As described above, the received signals are monitored asto any variation of predetermined signal parameters. If these variationsexceed a predetermined limit value, the solenoid 41 of the valve 4 istriggered, and the material mass is diverted from the conveying lineuntil the signal parameters are again below the predetermined limitvalue. Depending on the length of the measurement line section of theconveying line volume between the measurement line section and thevalve, and on the conveying speed, the valve 4 remains switched overbeyond this point of time until the material mass tested in themeasurement line section and showing signal parameters that exceed thelimit values is removed from the transport flow.

The amplitude of the received signal compared with the amplitude of thetransmitted signal can be easily evaluated as signal parameter. Providedthere is no foreign body in the material mass, the received signal isbasically free from interferences and only affected by the acousticcharacteristics of the material mass. In order to be able to testmaterial masses of differing consistency and showing different acousticcharacteristics, the limit values for the deviation of the receivedsignal from the transmitted signal are preferably adjustable. Theadjustment of these values can be made automatically at the beginning ofthe conveying process, e.g. by adapting the limit values to the soundabsorption of the material mass.

If the transported material mass contains a foreign body, either thereceived signal is attenuated by an increased absorbing effect or thetime of flight is reduced by a premature reflection. This interferencein the signal intensity or variation of the time of flight is detectedand evaluated in the signal processing unit 5. Since the transmittersare preferably operated in pulsed mode, the evaluation in view of areduction of the signal time of flight caused by a reflection from aforeign body is also possible as against the reflection from thereflector.

In one realized appliance, an ultrasound module with several channelswas used, which can be used with four pairs of test devices in atransmission technique. The measurement was taken in sequentialmultiplex operation. Each testing channel was provided with a blind withan amplitude checking device. Reinforcement and thresholds were adaptedto provide an optimal rate of recognition of foreign bodies. Amicrocontroller serves for control and evaluation.

The repetition frequency of the ultrasound measurement could becontrolled via the control surface. The impulse following frequencyamounted to a maximum of 4 kHz in total, which is equal to a rhythm of 1kHz for four channels. The measurements took place in a frequency areaof between 0.1 and 20 MHz. Within the blind, the maximum values(positive and negative half-wave) were measured. The blind was stated inbetween 10 μs and 30 μs and had a width in the area of 3 to 6 μs.

The evaluation was done automatically, where the reinforcement and theevaluation threshold were manually adjustable in each channel. Thefinish of the event was activated as soon as the threshold had beenpassed n times (n: any value between 1 and 256).

If the material mass to be tested shows e.g. a very irregularconsistency, which results in a stronger variation of the intensity ofthe received signal, the speed of an amplitude variation can also beused as an additional or alternative signal parameter, especially whencomparing ultrasonic signals received successively.

An especially large measuring range is obtained if the amplitudes of thetransmitted ultrasonic signals are continuously readjusted so that theamplitude of the received signals remains constant, with the manipulatedvariable now being evaluated as a signal parameter.

As the transmitted ultrasonic signals pass through the measurement linesection twice in the execution type shown here, an increased sensitivityis achieved as opposed to the alternative in which the transmitters andreceivers are positioned on the one or the other side of the measurementline section.

FIG. 2 shows a flow diagram of the operational mode of a device fordetecting and separating foreign bodies from a conveyed material mass.The primary task is to find out if there is a foreign body or not. Assoon as a foreign body is detected, a test is carried out to find outwhether the conveyed material volume dV following the foreign bodydetection is equal to a volume of the conveying line between themeasurement line section and valve (clearance volume Va). If thiscondition is met and the material mass containing the foreign body hasreached the valve, the pump operation is stopped and the valve isopened. As soon as the valve is open, the pump is again switched on andoperated until the conveyed material volume dV is equal to the dischargevolume Vb. If this condition is met, the pump is again stopped and thevalve Is switched back to its original position. After reaching thisswitching position, the pump is again put into operation until a newforeign body is detected. The volumes Va and Vb can be preset in anappropriate manner in this connection.

The device according to invention can be easily combined with a systemfor mixing, filling and/or packing of homogeneous and inhomogeneousfoods.

The principle according to invention is also suitable for detectingforeign bodies, e.g. bones or fish bones in meat or fish, i.e. mainly insolid masses.

LIST OF REFERENCE MARKS

1 conveying line

2 measurement line section

3 pump

4 valve

5 signal processing unit

21 ultrasonic transmitter

22 ultrasonic receiver

23 reflector

41 solenoid valve

We claim:
 1. A method of detecting the same or different foreign bodiesin viscous or liquid foodstuff masses in receptacles in which saidfoodstuff masses contain lumpy particles by the reflection or absorptionof sound, the method comprising the steps of: (a) conveying thefoodstuff mass at a predefined speed through a measurement line section;(b) transmitting at least one ultrasonic signal having a predeterminedamplitude through the foodstuff mass as the foodstuff mass passesthrough the measurement line section, said receptacles acting as atransmitting medium for acoustic signals; (c) receiving the transmittedultrasonic signal after it passes through the foodstuff mass and anychanges in the transmitted signal caused by reflection or absorption bya foreign body; (d) comparing at least one received ultrasonic signalwith at least one transmitted ultrasonic signal; (e) detectingvariations of at least one predetermined signal parameter between thereceived transmitted and reflected ultrasonic signal and the transmittedultrasonic signal; (f) generating an activation signal when thevariation in the pre-determined signal parameter exceeds or falls belowa predetermined limit value; and (g) interrupting or diverting thetransportation of the foodstuff mass when the activation signal isgenerated.
 2. The method according to claim 1, wherein the predeterminedsignal parameter is the amplitude of the ultrasonic signals.
 3. Themethod according to claim 1, wherein the predetermined signal parameteris the speed of the amplitude variations of several of the ultrasonicsignals received successively.
 4. The method according to claim 1,wherein the predetermined signal parameter is the time of the flight ofthe ultrasonic signals between an ultrasonic transmitter and anultrasonic receiver.